1. Field of the Invention
The present invention relates to a guide rail mechanism for a bonding apparatus.
2. Prior Art
Conventionally, the guide rail mechanisms used in bonding apparatuses such as die bonding apparatuses, wire bonding apparatuses, etc. include, as shown in FIGS. 5 and 6, a pair of guide rail sections 2A and 2B which guide both sides of a workpiece such as a lead frame 1. Since these guide rail sections 2A and 2B have more or less the same structures, the same or corresponding members will be described using the same reference numerals.
A pair of width adjustment guides 4 which extend in the direction of width of a lead frame 1 being conveyed are disposed on the upper surface of a stand 3, and a slider 5 moved by a driving means (not shown) is slidably disposed on each of the width adjustment guides 4. A sliding block 6 is provided on the slider 5, a supporting block 7 is installed on the sliding block 6, and a guide rail stand 8 is provided on the inner surface of the supporting block 7. Here, the phrases the "direction of width of the lead frame 1" and the "inner surface of the supporting block 7" are meant to be relative to the direction of the position of the heating block 14 (described later) which is located substantially in the middle of the pair of the guide rail stands 8 as shown in FIG. 5. A screw shaft 9 provided in a vertical direction is formed with an internal thread 9a in its upper portion is fastened to each of the guide rail stands 8. A rail height adjustment spacer 10 and a guide rail 11 are provided over the screw shaft 9 of each guide rail stand 8.
Furthermore, a spring 12 is mounted on a portion of the screw shaft 9 extending out of each guide rail 11, and a bolt 13 is screwed to the internal thread 9a of the screw shaft 9. As a result, the rail height adjustment spacer 10 and guide rail 11 are fastened in place by being pressed against the guide rail stand 8 by the spring 12. Furthermore, the heating block 14 referred above is disposed between the guide rails 11 so as to heat the lead frame 1. The heating block 14 is moved vertically by a driving means (not shown).
Guide rail mechanisms described above are described in, for instance, Japanese Patent Application Laid-Open (Kokai) Nos. S55-26696 and S60-63935 and Japanese Patent Application Publication (Kokoku) No. 63-56121.
In the above prior art, the lead frame 1 is fed along the guide rails 11 to a bonding position (not shown) by a feeding claw (not shown). After the positioning, bonding is performed by a bonding apparatus (not shown) to the lead frame 1. In die bonding apparatuses, semiconductor pellets are bonded to the surface of a lead frame, and in wire bonding apparatuses, wires are connected between leads of a lead frame and pads on the semiconductor pellets bonded on the surface of the lead frame.
Thus, in bonding apparatuses, semiconductor pellets are bonded to the surfaces of lead frames, and wires are connected between the leads of the lead frames and the pads of semiconductor pellets. In this case, the upper surface of the lead frame acts as a reference surface at the height position during bonding. Accordingly, if the thickness of the lead frame changes as a result of a change in the type of lead frame to be handled, it needs an adjustment. In other words, in cases where the lead frame to be handled is thicker than the previously handled lead frames, the height of the upper surface of the lead frame, i.e., the upper surface of the reference surface, is heightened. Accordingly, the guide rails 11 must be lowered so as to compensate the difference in thickness, thus keeping the height of the reference surface at a constant level.
More specifically, when the newly handled lead frames differ in thickness from the previously handled lead frames, it is necessary to use the rail height adjustment spacers 10 which have a thickness suited to the thickness of the newly handled lead frames. When the rail height adjustment spacers 10 are changed, the bolts 13 are first loosened and removed from the screw shafts 9, the guide rails 11 and rail height adjustment spacers 10 are both removed, new rail height adjustment spacers 10 are installed, the rail height adjustment spacers 10 and guide rails 11 are put back, and then the bolts 13 are tightened back in the screw shafts 9.
Especially in cases where the guide sections 11a of the guide rails 11 are angled C-shaped ("[") and angled reverse-C-shaped ("]") as shown in FIGS. 5 through 7, it has conventionally been necessary to replace the guide rails 11 entirely if the thickness t of the lead frame 1 changes greatly. Ordinarily, the thickness t, as seen in FIG. 7, of a lead frame is in the range of 0.1 to 0.4 mm. Accordingly, the height h of the guide sections 11a of the guide rails 11 is obtained by adding a clearance c to the thickness t of the lead frame 1 so that lead frame 1 can be conveyed smoothly. Consequently, in cases where the thickness t of the lead frame 1 is within the range of the height h of the guide sections 11a, it is necessary to replace only the rail height adjustment spacers 10, even if the thickness of the lead frame should change. However, in cases where the thickness t of the changed lead frame exceeds the height h of the guide sections 11a, the guide rails 11 must be replaced with guide rails that are suited to the changed lead frame.
In the above prior art, in cases where the thickness t of the lead frame 1 changes as a result of a change in the type of a workpiece (lead frame) to be handled, it is necessary to loosen and remove the bolts 13, replace the rail height adjustment spacers 10, put the bolts 13 back and then tighten them. In addition, the pair of guide rails 11 are installed so as to extend in the direction in which the workpieces are conveyed; accordingly, each one of the guide rail sections 2A and 2B is provided with two screw shafts 9 along the conveying direction, and springs 12 are mounted on the respective screw shafts 9 so that bolts 13 press the guide rails 11 and rail height adjustment spacers 10 against the guide rail stands 8 via the spring 12.
In other words, since each of the guide rails 11 have two screw shafts 9, two screws 12, two bolts 13, etc, when a lead frame of a different thickness is to be handled, four bolts 13 are loosened and removed, the rail height adjustment spacers 10 are replaced with other rail height adjustment spacers that suite the thickness of the lead frames to be handled, the guide rails 11 are put back, and then the bolts 13 are tightened back in the screw shafts 9. Thus, the adjustment requires a long period of time, resulting in a drop in productivity.